Diversity is known to influence single as well as multiple ecosystem functions (and/or services). Diversity-single-function effects (DSEs) frequently manifest themselves as saturating curves, while diversity-multi-functional effects (DMEs) often increase and then decline with an increasing threshold value. This DME pattern, known as the “Jack-of-all-Trades Effect” (JTE), is attributed to a lack of covariance among species’ individual influences over single ecosystem functions. While DSEs are sensitive to trophic structure, the impact of multi-trophic communities on DMEs has not been evaluated. In this study, we experimentally test whether key trophic levels affect DSEs and DMEs. We used data derived from an experimental grassland mesocosm study established at the Cedar Creek Ecosystem Science Reserve, Minnesota, USA. Plant diversity and the presence or absence of non-producer trophic levels (i.e., presence or absence of aboveground and litter macrofauna) were manipulated following a replicated multifactorial design. We measured three key ecosystem functions as response variables: primary productivity, soil water retention, and post-harvest biomass recovery. We employed a hierarchical Bayesian framework with a Michaelis-Menten function to model DSEs and parse out the impact of different trophic guilds on the JTE.
Results/Conclusions
Plant diversity, but not trophic structure, had a significant impact on all single ecosystem functions. The DME curve reflected the JTE for plant diversity treatments but the presence of one non-producer trophic level did not alter the DME curves. However, the presence of both trophic groups influenced both the DME and the JTE. We hypothesize that a decrease in the complementarity between plant species in the presence of aboveground and litter macrofauna lessens the observable JTE. Our results suggest that non-producer trophic levels impact ecosystem multifunctionality in ways that may not be detectable from measurements of single ecosystem functions. Assessments of ecosystem stability and threats to ecosystem health, therefore, need to consider trophic diversity to derive more realistic estimates of the impacts of biodiversity loss on the functions and services ecosystems provide.